175. Congenital Malformations of The Vestibulocochlear System

Malformations of the vestibulocochlear system can be classified into 3 different groups, corresponding
to the specific embryologic characteristics of each of the ear's 3 parts

LESIONS OF THE INTERNAL EAR

Cochlear

Rubella in the second month of pregnancy is often a cause of lesions here since this is when the internal
ear differentiates

The epithelium of the cochlea and vestibule is altered, but the organ of Corti has some intact regions,
so that children affected do perceive some deep frequencies

The semicircular canals: few malformations are known, although some have been seen with the use of thalidomide

LESIONS OF THE MIDDLE EAR: these usually involve the ossicles

After an infection, the mesenchymal plate separating the ossicles may become sclerotic, impede movement,
and may result in total deafness

Congenital fixation of the stapes results in severe congenital conductive deafness, although the remainder
of the ear is normal. The stapes is fixed to the bony labyrinth

May be due to a failure of differentiation of the annular ligament of the stapes

Defects of the malleus and stapes are often associated with abnormalities of branchial arch I, , in
hypoplasia of the mandible as seen in micrognathia

MALFORMATIONS OF THE EXTERNAL EAR

May result from the absence or nonunion of the primordial tubercles

Major variations of the auricle have been associated with serious internal abnormalities, such as kidney
malformations

Abnormal position of the ear: usually associated with abnormal mandibular development, such as agnathia
or micrognathia

Instead of moving to the sides of the head, the ears develop at the site of the primordia namely, at
the level of the first branchial groov Thus, at birth, the ears are seen at the angle of the missing
jaw (otocephalus)

Auricular appendages or tags are common and due to accessory auricular hillocks

Absence and hypoplasia of the auricles are rare and are associated with arch I syndrome where there
is a failure of the auricular hillocks to develop (anotia) or they are suppressed in their development
(microtia)

Auricular sinus and fistulas: sinuses are usually preauricular and fistulas connect the exterior with
the tympanic cavity

Atresia of the external auditory meatus: failure of the meatal plug to canalize

Congenital deafness is usually associated with deaf-mutism

MAY BE CAUSED BY

An abnormal development of the membranous and bony labyrinths

Malformations of the eardrum and ossicles

In extreme cases, the tympanic cavity and the external auditory meatus are completely absent

OTHER CAUSES OF DEAFNESS

Hereditary

Environmental and other factors affecting the mother early in pregnancy

Rubella virus, affecting the embryo in weeks 7 and 8 of development, can cause severe damage to the
organ of Corti; diabetes; erythroblastosis fetalis; hypothyroidism; toxoplasmosis; and x-radiation

MAJOR VARIATIONS OF THE AURICLE have been associated with serious internal abnormalities, such as seen
with kidney malformations